The present invention relates in general to a method and apparatus for use in creating or reproducing an audiovisual product. In particular, the present invention relates to a method and apparatus for use in controlling access to an audiovisual product, through the use of scrambled video streams.
It is desired to control access to an audiovisual product. In particular, it is desired to restrict opportunities that currently exist for audiovisual content to be viewed or otherwise accessed without authorisation.
In general terms, audiovisual content such as a movie or other presentation is formed by gathering together many small sections or clips of raw audio and visual content. This is usually termed an “authoring” process wherein the raw sound clips and video clips are progressively assembled and edited together to form the finished audiovisual product. The audiovisual product is then recorded on some form of recording media. Traditionally, this would be an analogue medium such as celluloid film or analogue video tape (e.g. VHS format video tape). More recently, it has become possible to record audiovisual content onto random access media including in particular optical disk media such as DVDs, or other forms of random storage such as magnetic hard drives. These random access media have many advantages in terms of size, data capacity, playback speed, image quality and so on. However, a disadvantage has also been identified in that it is relatively easy to view or otherwise access a stored audiovisual product, without authorisation.
An optical disc is a convenient storage media for many different purposes. A digital versatile disc (DVD) has been developed with a capacity of up to 4.7 Gb on a single-sided single-layer disc, and up to 17 Gb on a double-sided double-layer disc. There are presently several different formats for recording data onto a DVD disc, including DVD-Video, DVD-Audio, and DVD RAM, amongst others. Of these, DVD-Video is particularly intended for use with pre-recorded video content, such as a motion picture. As a result of the large storage capacity and ease of use, DVD discs are becoming popular and commercially important. Conveniently, a DVD-Video disc is played using a dedicated playback device with relatively simple user controls, and DVD players for playing DVD-Video discs are becoming relatively widespread. More detailed background information concerning the DVD-Video specification is available from DVD Forum at www.dvdforum.org, and elsewhere.
The DVD-Video specification contains a number of built-in copy-protection features that aim to protect the audiovisual data content of the disc. These include Content Scrambling System (CSS), used to encrypt blocks of audio-video data to prevent such data being played separately from the DVD-Video presentation; and Macrovision Copy Protection, used to prevent video being copied using recording devices. Both of these systems are interpreted by the DVD-Video player that performs the appropriate function during playback. While these approaches are effective in protecting data content for average consumers, “reverse engineers” who are skilled and motivated to create copies of discs or parts of discs now easily defeat both systems.
A problem has been identified in that, within the DVD-Video specification, there are no built-in facilities by which content can be held securely on a disc, whilst remaining out of the reach of a reasonably competent reverse engineer. As an example to illustrate this problem, DVD-Video discs sometimes contain so-called “Easter Eggs” which are hidden data on a disc that are accessed such as by inputting a particular key combination (e.g. press a “left arrow” key within 5 seconds of a certain menu appearing). A reverse engineer can easily access such content without knowing the key combination, simply by extracting the relevant audio-video objects directly from the disc. There are a number of DVD-Video interrogation software packages available that can be used to ‘rip’ each of the individual video presentations on a disc. See, for example, www.dvd-ripper.com, amongst many others.
U.S. Pat. No. 6,161,179 (WEA Manufacturing, Inc) discloses a key-based protection method for light-readable discs, wherein a disk player provides a unique key each time a disk is played. The user communicates the unique key to a transaction service, and receives an unlock key in return. The user communicates the unlock key to the disk player. The disk player then confirms that the unlock key and the unique key have a predetermined relationship, before playing the disk. This known protection method allows pay-per-view or other pay-per-use commercialisations of an audiovisual product distributed on a light-readable disk, such as in a DVD-Video format.
There are a wide range of applications where a greater level of security and protection is required over and above that afforded by the known copy-protection approaches. These problems arise not only in relation to DVD-Video format optical disks but occur in many other environments, especially where audiovisual content is recorded onto a random access storage medium.